1. Field of the Invention
The present invention relates to a fluid pump, which has a pressure pulsation reducing function.
2. Related Art
There are two types of fluid pumps such as a fuel pump for a vehicle, one being a positive displacement type such as a trochoid gear pump and a roller pump and the other being a non-displacement type such as a turbine (Wetsco) pump.
In the displacement type pump, fluid is sucked and discharged by variations in the displacement of a pump chamber. It has therefore a higher pumping efficiency, while causing a large pressure pulsation in the discharged fluid, large noise and large vibration. In the non-displacement type pump, on the other hand, fluid is sucked and discharged by rotation of a turbine (impeller) within a pump casing. As the displacement of a pump chamber is not varied, it causes less pressure pulsation in the discharged fuel, less noise and less vibration.
In the case that the displacement type pump is used, a damper device is provided at a fluid discharge side or a fluid pipe is formed by an elastic material to reduce the pressure pulsation, noise and vibration. Particularly, in the case that the displacement type pump is used as a fuel pump for a vehicle, a sound-shielding material is attached to a vehicle chassis to shield noise. Those will result in rise in the production cost.